Where is the prostate/how to hit it?

Hi guys (and girls). I bought my man an anal vibrator and the lady in Ann Summers told me it would hit his prostate. She gave me a bit of an anatomy lesson but when it came to it I just couldn’t find his prostate. He said he enjoyed the experience but there was nothing like “omg that’s the spot” kind of orgasmic feeling. How do I do it? How do I angle? Is it deep in there or what? Any guys here that have experienced it and what did it feel like to you? So I know what to expect. Thanks